1. Field of the Invention
The present invention relates to a micropump for delivering fluid at a low and controllable flow rate.
2. Description of the Prior Art
Science and engineering have been devoted to building machines that mimic human's functionality to expand our reach. The Industrial Age came about due to the invention of steam engine which freed human from laborious muscle works. With the advent of electronics, computers are revolutionizing the Information Age. Advances in microelectronics processing have opened up a far reaching capabilities in microengineering.
In recent years, there has been an explosion of interest in the field of integrated MicroElectroMechanical Systems (MEMS). The field is still so new that there is no commonly accepted definition of the field among researchers. Instead of fashioning devices that simply shunt electrons, moving devices are fabricated. While integrated circuit technology is essentially a two-dimensional or planar process. MEMS works in a three dimensional process. Because much of the key process is not radically different from fabricating microelectronics elements, many essential techniques can be simply copied.
Rooted back in the early research effort on materials and processing for the fast emerging field of integrated circuits, the late 1960's and early 1970's saw the effort in developing integrated sensors. After early attempts to make temperature and pressure sensors, visible image arrays were produced in large volume. After years of steady improvement, today visible image arrays rival the resolution of photographic films and promise to revolutionize the field of photography. Though they represent some of the largest chips made. Only a few processes and packaging techniques go beyond standard integrated circuit manufacturing.
1970's saw considerable advances in bulk micromachining. The emergence of preferential etch, and impurity based etch-stops took silicon based sensors out of laboratories into mass production. Pressure sensors led the way. Much attention was concentrated on preferential etch and sealing technique to make pressure sensors a reality on silicon. Late 1980's surface micromachining led to the development of a series of AC resonant sensors. Gradually, accelerometer and flowmeters joined pressure sensors as high-volume production devices.
Today, bulk and surface micromachining, in combination with wafer-to-wafer bonding and electroforming technologies offer a designer a rich array of processes for the creation of micromechanical structures in batch and with high precision. It has been established that micromachined sensors can be produced with high yield. They can be merged with integrated electronics, both in monolithic and multi-chip hybrid assemblies. These devices are widely used in high performance instrumentation and control system. To date, VLSI interface circuitry with digital signal processing has pushed some sensors to reach 16-bit accuracy and feature self-testing and digital compensation possible for commercial mass production.
Since micromachined sensors are passive devices, a complete mechanical system is not readily implemented. In order to complete the system, actuators, namely machines that cause other devices to move, are badly needed. In 1988, combining surface micromachining, the emergence of electrostatic actuators were widely researched. Later, other actuation methods such as thermal and resonant actuation also demonstrated their possibilities.
With the addition of microactuators to microsensors and microelectronics interface circuitry, most of all the elements for a complete MEMS were in place. However, due to the complexity of microactuators, integration has proven to be difficult. Microactuators which were being produced were never fully satisfactory for practical applications. To date, electrostatic microactuators remain as the accepted means of actuation in microscale. Only recently has the possibility of magnetostatic microactuators been realized with reasonable success.
The requirements for an ideal microactuator can be overwhelming. A microactuator has to be able to transfer its driving energy to other devices. A low loss energy transmission must be incorporated into the system. The driving voltage for the microactuator must be compatible with integrated circuits, which can mean well below 15 volts, in order to be controlled by on chip electronics. Reliability of the microactuator should be as unquestionable as the driving electronics themselves. And last, the fabrication process should be compatible with electronics fabrication processes.
What is needed to address these requirements is a completely different approach to achieve microactuation.